The purpose of this project is to evaluate the carcinogenic potential of medical treatment with drugs. Since many cancer patients are exposed to both radiation and cytotoxic agents, these studies are a logical extension to the Branch's study of radiation-induced second cancers. In addition, other non-therapeutic drugs are studied when of special interest. The Branch also conducts studies of multiple primary cancers to generate hypotheses about host and environmental determinants of specific cancers. Populations under study include cancer patients reported to population-based cancer registries (especially the SEER program), persons treated at major institutions, and those treated in randomized clinical trials. Additional details on collaborative projects can be found in Project No. Z01CP04411-GEB, "Carcinogenic Effects of Therapeutic Drugs" and Project No. Z01CP04418-GEB, "Studies of Persons at High Risk of Cancer." The risk of bladder cancer after cyclophosphamide therapy for non- Hodgkin's lymphoma was significantly increased with risk dependent upon dose. Drug therapy for NHL was associated with a high risk of leukemia, however, risks were low following cyclophosphamide regimens. Bone marrow transplant recipients had a high risk of developing NHL, Hodgkin's disease (HD) and solid tumors, with excess risks linked to immune suppression and high dose radiation. The risk of lung cancer was associated with high dose radiotherapy among patients with breast cancer and HD. Radiotherapy was linked to a significantly increased twofold risks of nonlymphocytic leukemia among patients with uterine corpus cancer. Women receiving adjuvant hormonal therapy for breast cancer, primarily tamoxifen, had a significantly increased risk of uterine corpus cancer. However, there was little evidence that tamoxifen affected the incidence of any cancer of the digestive tract as previously reported.